In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features of the third-generation system, which are based on W-CDMA (Wideband Code Division Multiple Access), are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (see, for example, Non-Patent Literature 1). In LTE, as multiplexing schemes, OFDMA (Orthogonal Frequency Division Multiple Access), which is different from W-CDMA, is used on downlink channels (downlink), and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used on uplink channels (uplink).
In the third-generation mobile communication system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the system of LTE (Release 8), which is referred to as the 3.5-th generation, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A or Release 10)). In the future, these multiple mobile communication systems are expected to coexist. There is a demand, for the LTE-A system that is currently under study, to guarantee backward compatibility with LTE.